Electrophotographic process utilizing organic photoconductors



United States Patent 3 148 982 ELECTROPHOTOGRA PHI C PROCESS UTILIZING ORGANIC PHOTOCONDUCTORS Patented Sept. 15, 1964 ice Theofiel Hubert Ghys, Knotich-Antwerp, Robert Joseph wherein Noe, Berchem-Antwerp, and Paul Maria Cassiers and 5 Jean Marie Nys, Mortsel-Antwerp, Belgium, assignors R represents an alkyl group, an aryl group, an aralkyl to (ievaert Photo'productell Mortsel'Antwel'l group, a substituted alkyl group, a substituted aryl group Belgium a company of Belgium or a substituted aralkyl group No Drawing. Filed Apr. 11, 1960, Ser. No. 21,098

6 Cl i (C1, 96 .1) 1 R represents a hydrogen atom, an alkyl group, a sub- 0 stituted alkyl group, an alkylmercapto group, an aryl The present invention relates to an electrophotograph c group a substituted aryl group, a heterocyclic group materlal, and more particularly to an electrophotographic or substitutpd heteroc CH6 mu ,7 material consisting of a support and a photoconductive V y g 1 layer Which contains an rganic photoconductive sub- 3 and 4 (equal dlfiefent) a r presents a hydrogen stance or which consists of an organic photoconductiveatom, yl group, an aryl group, an aralkyl g p substance. a substituted alkyl group, a substituted aryl group or Electrophotographic materials are already known which a Substituted y p; consist of a support and a photoconductive layer contain- Ar represents the non-metallic atoms necessary to commg as Photoconductor inorganic Substance Such as plete an aromatic nucleus selected from the group conselglium or 1iinc gilv xide or 211x11 organi 1 su t Such as sisting of a benzene nucleus and a naphthalene nucleus; g gfilg 52 me or a eterocyc 10 compound of a X represents an oxygen atom, a sulphur atom, a selenium Now we have found that an electrophotographic matep a i group or a mtmgen atom Subsmutes rial with particularly favorable properties and suitable Wlth an R1 radlcal; to be used in the application of the most widely varying Y represents gy atom, a sulphur atom, a selemum electrophotographic reproduction methods is obtained atom, all afyllmlno g p an alkylslllphonlum pif in the manufacture of the photoconductive layer compounds are used h i one of the general f l Some compounds according to the above formula which R1 seemed to be particularly suitable for the manufacture of the v electrophotog-raphic material according to the f present invention are given hereinafter in the table.

,0 C=CHC=Y I I Rr-C ?=CH?=Y and 131 R aCX R, -o-X TABLE Compound R3 R4 R1 R2 X Y 1 I CHa CaHs S 0 2 CzHs CeHs S O 3 CH3 CzHs S i 0 4 CH3 CsHs 0 H36 CH3 5 CH3 CoHa s 0 CH3 CH3 8 r O 7 p CH3 CaHs S O s 6 CH3 CaHs I 's o 9 g 2 02135 CH3 Se 7 M0 7 TABLE-Cniinued Compound R3 R4 R1 R2 X Y 1 1O CH3 05115 36 0 11 2 -(OH:)z0C0 co s Se 0 12 C H: C2H5 s S 13 C2H5 CH3 S 14 C2 5 Q s S 15 CH3 02115 S S 16...; C2115 C5135 S S 17 j CH3 CH3 S S 18 M 0113 0111 s s 19 C 2115 CH S s 20 u CH3 SCH; S S+OHs1CH3COr 21 011 15 0:13 Se S 22 021157 Ca e; Se S 23 02115 CuHs Se 3 24 C211 H O N-CaHs 25 (32115 H O N-Cs s 2a 2 02115 11 o N-CuHs I Ha C CH:

27 0211 7 H r 0 NCaHs 28 CaH; H O N-COHs 29 4 02115,v H s N'CfiH6 30 4 02115 H Se N-CuHs a1 02115 H 051:013 7 Noflm The omega-ketones from this table can be prepared according to the methods described in the US. patent specification 2,468,577 and by A. Van Dormael and Th. Ghys in Bull. Soc. Chim. Belg. 57 (1948), 24. The omegathioketones from the table can be prepared according to the method described in the US. patent specification 2,356,569.

For the manufacture of the elect-rophotographic material according to the present invention, a photoconductivelayer containing at least one of the compounds according to the above general formula or mainly consisting of at least one of the compounds according to the above general formulae is applied to a suitable support.

The photoconductive layers according to the present invention can contain besides one or more of the compounds according to the above general formula stillone or more other photoconductive compounds with similar or difierent photoelectric-, mechanical or other physical properties; moreover, there can be present in the photoconductive layer other compounds which confer the properties desired to the photoconductive layer and/or to the composition wherefrom this layer is formed.

Thus, in the manufacture of the photoconductive layers according to the present invention one or more macromolecular compounds can be added as binding agents to the composition wherefrom the photoconductive layer is formed; preferably, macromolecular compounds with high specific resistivity (i.e. with a specific resistivity higher than ohm.(cm.) are used for this purpose; macromolecular compounds particularly suitable as binding agent for the photoconductive layers are e.g. natural resins, such as dammar resin, elemi-resins, gum arabic, manilla gum and sandarac resin; micro-crystalline waxes; modified natural substances such as cellulose diacetate and cellulose triacetate, cellulose acetobutyrate, ethyl cellulose, ethyl cellulose stearate or other cellulose derivatives pentaerythrite polyesters or other modified colophonium resins and ester gums; polymerisates such as polyethylene, polystyrene and copolymers of styrene, polyvinylacetate and copolymers of vinylacetate, polyvinylacetals of formaldehyde, acetaldehyde, butyralde hyde, polyacrylic acid esters and polymethacrylic acid esters and coumarone-indene resins; and polycondensates such as glycerol-phthalate resins or other glyceryl polyesters, alkyd resins, polyethylene glycol esters, diethylene glycol polyesters, formaldehyde resins and silicone resins; particularly good results can be attained by using the polyesters described in US. patent application Serial No. 702,252, filed December 12, 1957, and polysulphonates such as described in US. patent application Serial No. 797,587, filed March 6, 1959.

In the choice of a suitable binding agent one is not limited to previously polymerized compounds; indeed, also low molecular compounds can be used or mixtures of low and high molecular compounds, or semi polymerisates which are polymerized or condensed in .situ or undergo cross-linking according to one of the methods known in polymer chemistry.

If desired, suitable plasticizers such as dibutylphthalate,

dimethylphthalate, dimethylglycolphthalate, tricresylphos-.

phate, triphenylphosphate, monocresyldiphenylphosphate, etc., in quantities amounting to 10 to by weight of the amount of binding agent used can be added to .the compositions for the formation of the photoconductive layers containing abinding agent.

Further can still be used otheradditiveswell known in,

the coating technique suchras for instance pigments, compounds which influencethegloss and/or the resistivity,

compounds which counteract the aging and/ or the oxidation or which influence the thermal stability of the layers.

In the choice of these additives, those are preferred which. little or not reduce the dark-resistivity of the photocom.

ductive layer.

The thickness of the layers is not critically established:

but 'is determined by the requirement of each separate case. Good results are attained with electrophotographic layers the thickness of which varies between 1 and 20 and preferably between 3 and 10 for layers which are too thin possess an insufiicient insulating power whereas layers which are too thick require long exposure times.

Finally, according to the present invention compounds which themselves possess either or not photoconductive properties and which cause an increase of the general sensitivity and/or of the sensitivity to electromagnetic rays from a determined part of the spectrum can also be present in the photoconductive layers.

Thus, for example, the general sensitivity and/or the sensitivityto electromagnetic rays from the visible part of the spectrum can be enhanced by adding to the composition from which the electrophotographic layer is to be formed one or more of the sensitizing compounds listed in the copending US. patent application Serial No. 11,129, preferably in a quantity of 0.1 to 5% in respect of the amount of the photoconductive compound according to the above general formulae. 7

In the manufacture of the electrophotographic material according to the present invention is preferably used as support for the photoconductive layer an electrically con ductive plate or sheet, or an insulating plate or sheet provided with an electrically conductive layer. Under electrically conductive plate, sheet or layer is understood a plate, sheet or layer the specific resistivity of which is smaller than that of the photoconductive layer, i.e., in

general smaller than 10 ohm. cm. Supports the specific resistivity of which is smaller than 10 ohm. cm. are preferably used.

Suitable insulating, plates are e.g., glass plates; these plates must be coated with a conductive layer, e.g., with atransparent layer of silver, gold or stannous oxide deposited thereon e.g. by vacuum evaporation.

Suitable insulating sheets are for instance films of synthetic macromolecular substances with high specific resistivity such as for instance the polysulphonates described and claimed in US. patent application Serial No. 797,587 for Production of Linear Aromatic Polyesters, filed March 6, 1959, polyesters such as those described and claimed in US. patent applications Serial No. 702,252, for Production of Linear Aromatic Polyesters, filed Decem ber 12, 1957, Serial No. 725,498, for Production of Linear Aromatic Polyesters, filed April 1, 1958, and Ser. No. 731,874, for Production of Linear Aromatic Polyesters, filed April 30, 1958, polystyrene, polyethylene, cellulose esters, etc., or sheets of paper with high specific resistivity. These insulating sheets must be provided with a conductive layer e.g. a thin metal sheet, with a layer comprising a metal powder dispersed in. the smallest pos-- sible amount of binding agent, or with a. thin hydrophiliclayer comprising a hygroscopic and/or antistatic compound and ahyclrophilic binding agent. Suitable hygroscopic and/ or antistatic compounds are for instance glyc-- erine, glycol, polyethylene glycols,. calcium, chloride, sodium acetate, condensation products of maleic acid and.

Nemours & Co. (Inc.), Wilmington, Del.), lyophilic di-.L

alkylpolyoxyalkylene.phosphates sucli as Victawet 12 (trade name of Victor Chemical Works, Chicago, Ill.) and polyoxyalkyleneamides such as Ethomid HT/60 (trade name oLArmour and Company, Chicago, Ill.).

Suitable; hydrophlilic binding agents are for instance gelatin, glue, polyvinyl alcohol, methylcellulose, c'arboxy methylcellulose, cellulosesulphate, cellulose hydrogen phthalate, cellulose-acetatesulphate, hydroxye'thyl .cellu ,lose, polyacrylic acid or colloidal silica; for obtaining a good adhesion of the hydrophiliclayer and the hydrophobic polymeric sheet, the polymeric sheet can be provided with a suitable subbing layer such as for instance one of the subbing layers described in US. patent application Serial No. 509,333, for Manufacture of Photographic Film, filed May 18, 1955 (for polyester films), the British Patent 819,592 and British patent application No. 41732/58, filed December 24, 1958 (for films of polystyrene and substituted polystyrene), US. patent application Serial No. 826,129, for subbing Method for Polyalkylene Materials, filed July 10-, 1959, the Belgian Patent No. 569,129 (for polyalkylene films), US. Patent 2,867,542 (for cellulose ester films), and the Belgian Patent No. 573,005 (for hydrophilic layers with polyvinyl alcohol as binding agent).

Suitable conductive plates are for instance plates of metals such as aluminum, zinc, copper, tin, iron or lead.

Suitable conductive sheets are for instance films made of polymeric substances with low specific resistivity such as for instance polyamide films or paper sheets with low specific resistivity. Good results can be attained by using paper sheets containing hygroscopicand/or antistatic substances as described above. These hygroscopic and antistatic substances are preferably incorporated into the paper sheets during the paper manufacturing process either by adding them to the paper pulp or by an aftertreatment, before or after calendering the paper sheets.

These substances can likewise be incorporated into the paper sheets by applying to the raw paper stock a composition containing the hygroscopic and/or the antistatic substances and a hydrophilic binding agent as described above.

It was likewise stated that particularly good results are attained when using paper sheets provided with a coating of a polymeric substance in order to obtain a smooth surface and to prevent the organic liquid wherein the photoconductive substance is dissolved, from penetrating within the paper sheet. This coating, however, must not prevent the carrying-off of the electrons from the exposedimage areas during the irradiation. Suitable coatings are for instance coatings with a thickness of 2 to 10p and composed of one or more of the macromolecular compounds described above as binding agent for the photoconductive compound.

Besides the usual paper sorts canlikewise be used synthetic paper sorts such as those prepared from polyesters,

e.g. Dacron and Terlenka-fibers (trade names for polyester fibers from terephthalic acid and glycols manufactured by E. I. du Pont de Nemours & Co. (Inc), Wilmington, Del, resp. Algernene Kuns tzijde Unie N.V., Arnhem, Netherlands), from polyamide fibers such as Enka- Ion-fibers (trade name of Algemene Kunstzijde Unie N.V., Arnhem, Netherlands) or Nylon-fibers or from polyacrylonitrile fibers such as Orlon-fibers (trade name of E. I. du Pont de Nemours & Co. (Inc), Wilmington, Del). Before coating the photoconductive layers on such paper sheets, the latter are preferably impregnated with substances enhancing their conductivity, for instance polycaprolactam, the polyester of 2,5-di(p-hydroxyphenyl)-l,3,4-oxadiazole and 1-chloro-3-aminobenzene- 4,6-disulphochloride, a 'copolyamide of hexamethylenediamine, caprolactam, adipic acid and sebacic acid, N- methylene polyhexamethylene adipamide, or polyamides such as Ultramid 1C (trademark for a polyamide manufactured by Badische Anilin- & Soda-Fabrik A.G., Ludwigshafen (Rhine).'

In practice, the compounds according to the abovegeneral formulae either alone or together with other additives such as for instance bindingagents, compounds which enhance the sensitivity etc. are preferably first dissolved or dispersed in a suitable organicsolvent such as for instance benzene, acetone, methylene chloride, dioxane, dimethylformamide or glycol monomethylether, or in a mixture of two or-more of such solvents. The solution or dispersion thus obtainedis uniformly spread ruary 4, 1960. According to the method as described in said patent application, a solution of the photoconductive on a surface of a suitable support, for instance by centrifuging, spraying, brushing or coating whereafter the layer formed is dried in such a way that a uniform photoconductive layer is formed on the surface of the support.

A particularly interesting method for applying to asupport a photoconductive layer containing little or no binding agent is described in US. patent application Serial No. 6624, for Electrophotographic Material, filed Febsubstance is applied to the support in such a Way that a micro-crystalline layer is formed; for this purpose is preferably used a heated, strongly concentrated solution of the photoconductor in a strong organic solvent and the layer formed is preferably quickly dried for instance in a hot air current or by action of infrared radiation.

Electrophotographic materials according to the present discharge of a capacitor. A positive charge applied at the rear side of the printing material gives about the same result as a negative charge at the front side.

The electrophotographic material is thereafter imagewise. exposed to a suitable electromagnetic radiation whereby the radiated parts of the layer are image-wise discharged and an electrophotographic latent image is obtained. The electrostatic latent image formed is then converted into a visible image either on the, electrophotographic material whereon the latent image was formed, or on a material onto which the electrostatic latent image was transferred for instance by application of the method as described in the Belgian Patent No. 529,234.

The conversion of the original or transferred latent image into a visible image can occur. according to one of the techniques known in electrophotography wherein use is made of the electrostatic attraction or repulsion of finely divided colored substances which for instance are present .in a powder or powder mixture, in an electric in? sulating liquid (for instance inthe form of suspension) or in a gas ("for instance in the form of aerosol), or of finely divided colored liquid drops which are for instance present in an electrically insulating liquid (for instance in the form of dispersion) or gas (eg in the form of aerosol).

Bysuitable choice of the-sign of the charge of the developing powderor developing liquid a negative or positive print can be obtained at will from anyoriginal.

If both the printing material and developing powder or developing liquid bear the same charge sign, the powder will only adhere to the discharged areas and a print (positive/positive) is obtained with the same image value as the original. If the sign of the material and of the developing powder or developing liquid is different, the image values become reversed (negative/ positive).

' Besides development according to the methods generally known in the electrophotography, also other techniques can successfully be used for instance by applying the method according to the US. patent application Serial No. 856,357, for Development of Electrostaticv Latent Images, filed December 1, 1959, and US. patent application Serial No. 741,017, for Electrophotographic Process, filed June 10, 1958.

If a colored powder was used for making visible the latent image, thevisible image obtained can, if necessary,

be fixed according to one of the methods known in electrophotography, e.g. by heating, or it can be transferred onto another support, for instance according to the meth- 9 od described in the British Patent 658,699 (Can. Patent 518,430) and fixed thereon.

Evidently, the present invention is by no means limited to one or the other particular embodiment as regards the use of the new electrophotographic materials, and the exposure technique, the charging method, the

transfer (if any), the developing method, and the fixing method as well as the materials used in these methods can be adapted to the necessities.

Electrophotographic materials according to the present invention can be applied in reproducing techniques wherein different kind of radiations, electromagnetic radiations as well as nuclear radiations are used. For this reason, it should be pointed out that although the invention is mainly intended for being applied in connection with methods comprising an exposure, the term electrophotography wherever appearing in the description and the claims, must be broadly understood and comprises both xerography and xeroradiography.

The following examples illustrate the present invention without limiting, however, the scope thereof.

Example 1 A 90 g./sq. m. paper covered with an aluminum sheet of a thickness of 8 is coated with a layer from a solution consisting of equal parts of a solution in methylene chloride of Hostalit (trademark for a terpolymer of vinylchloride, vinylacetate and maleic anhydride manufactured by Farbwerke Hoechst A.G., Frankfurt am Main) and of a solution in methylene chloride of the compound 19 of the table. After drying this layer for h. at 50 C., the treated material is negatively charged with a corona apparatus. The electrophotographic material obtained is then exposed through a diapositive for 10 seconds with a 100 watt-lamp at a distance of 10 cm. The latent image formed is developed with a developing powder prepared as follows: 70 g. of gilsonite and 30 g. of carbon black are homogeneously mixed whilst heating and after cooling pulverized; 6 parts of this powder obtained are then mixed with 100 parts of iron filling.

Example 2 A aluminum plate is coated with a layer from a solution consisting of:

Polyester of 2,2'-di(p-hydroxyphenyl)-propane and fumaric acid prepared according to the method described in the Belgian patent specification 563,173 (U.S. patent application Serial No.

702,252, filed December 12, 1957) g 5 Methylene chloride cm. 100 Compound 23 of the table g 5 Example 3 A cellulose-acetate sheet coated with a thin silver layer of 1p. deposited thereon by vacuum evaporation is covered with a thin layer from a mixture consisting of equal parts of a 10% solution in methylene chloride of Hostalit (registered trademark) and of a 10% solution in methylene chloride of compound 18 of the table. After drying this layer for 15 h. at 50 C., the material treated is negatively charged with a corona apparatus. The electrophotographic material obtained is then exposed for 0.5 second through a transparent original with a 100 watt lamp at a distance of 10 cm. The latent image formed is then developed as in Example 1.

Example 4 A paper support covered with a thin aluminum layer is coated with a thin layer from the following solution:

Butvar (registered trade name for a polyvinylbutyral manufactured by Shawinigan Resins Corporation,

Springfield, Mass.) g 2.5 Methylene chloride cm. Compound 13 of the table g 5 Example 5 A paper support covered with a thin aluminum layer is coated with a thin layer from a 5% solution of Hostalit (registered trademark) in methylene chloride and next with a thin layer of a 10% solution in methylene chloride of compound 29 of the table. After drying this material for 15 h. at 50 C., it is negatively charged with a corona apparatus. The electrophotographic materialobtained is then exposed for 1.5 sec. through a diapositive with a 100 watt lamp at a distance of 10 cm. The latent image formed is developed with a tribe-electric powder such as in Example 1.

Example 6 A sheet manufactured from Mylar (registered trade name for sheets manufactured from polyethylene glycol terephthalate by E. I. du Pont de Nemours & Co. (Inc), Wilmington, Del.) and coated with a thin aluminum sheet of a thickness of 3p. deposited thereon by vacuum evaporation is covered with a thin layer from the following solution:

Butvar (trade name) g 5 Compound 30 of the table g 5 Methylene chloride cm. 100

R R R and R each is a member selected fromthe group consisting of a hydrogen atom, a lower alkyl group and a phenyl group;

Ar represents the non-metallic atom necessary to complete an aromatic nucleus selected from the group consisting of a benzene nucleus and a naphthalene nucleus;

X is a member selected from the group consisting of an oxygen atom, a sulphur atom, a selenium atom, a vinylene group and a lower alkyl-substituted.nitrogen atom, and

Y is a member selected from the group consisting of an oxygen, sulphur, selenium, arylimino group and a lower alkyl-sulphonium group, said organic compound being present in sufficien-t quantity to provide photoconductivity to said layer, to a light image whereby the light struck area is discharged, and developing said image of electrostatic charges with an electroscopic material.

2. The electrophotographic copying process of claim 1 wherein the organic compound has the formula 3. The electrophotographic copying process of claim 1 wherein the organic compound has the formula 4. The electrophotographic copying process of claim 1 wherein the organic compound has the formula i2 5. The electrophotographic copying process of claim 1 wherein the organic compound has the formula Se =OHCH=N 0 11 6. The electrophotographic copying process of claim 1 wherein the organic compound has the formula 5 \(3=CHC=O Cl I1\I References Cited in the file of this patent UNITED STATES PATENTS 2,356,569 De Smet Aug. 22, 1944 2,442,710 Riester June 1, 1948 2,586,164 Hensley Feb. 19, 1952 2,611,695 Thompson Sept. 23, 1952 2,656,271 Neugebauer et a1 Oct. 20, 1953 2,732,301 Robertson et al. Jan. 24, 1956 2,956,878 Michiels et al. Oct. 18, 1960 FOREIGN PATENTS j 562,336 Belgium May 13, 1958 7 214,444 Australia Apr. 11, 1958 1,177,936 France Dec. 8, 1958 1,188,600 France Mar. 16, 1959 586,894 Canada Nov. 10, 1959 OTHER REFERENCES Nelson 1.: Opt. Soc. Am.', vol. 46, No. 1, January 1956, pages 10-13;

Photographische Korrespondez 94 (1958), pages 3-11 and 19-26 (copy in Scientific Library). 

1. AN ELECTROPHOTOGRAPHIC COPYING PROCESS WHICH COMPRISES EXPOSING AN ELECTROSTATICALLY CHARGED PHOTOCONDUCTIVE INSULATING LAYER COMPRISING AN ORGANIC COMPOUND HAVING A FORMULA SELECTED FROM THE GROUP CONSISTING OF 